1. Field of the Invention
The present invention relates to a micropump serving as a small apparatus for supplying small amounts of fluid used in a fuel cell, medical equipments, a chemical analyzer, a microreactor, a biochemical chip and the like, and particularly relates to a method of manufacturing a check valve for preventing back flow of the fluid in this micropump.
2. Description of the Related Art
In a micropump for delivering small amounts of fluid, a check valve is often used to prevent back flow of the fluid. Under constraints of smallness and thinness, the check valve is required to be configured that a valve part has pretension so as to contact a valve receptor while applying urging force thereto so that the valve part satisfactorily seals the valve receptor to prevent the back flow of the liquid when only a force smaller than a constant pressure is acting.
The following patent documents disclose a mechanism (hereinafter referred to as a pretension mechanism) for applying pretension to a valve part of a check valve.
In the micropump disclosed in JP-A 02-308988, a technique is employed for integrally forming the valve part and a pressurized chamber including the valve part, and performing ultrasonic welding or adhering with an adhesive, the members constituting the valve part and the pressurized chamber, the valve receiving member including the valve receptor, and a vibrating plate vibrated by a piezoelectric element, with respect to each other.
JP-A 04-63973 discloses that in a micropump in which a silicon substrate formed with a diaphragm, a flow path and a valve part is sandwiched from both sides on a glass substrate, a projection made of polymeric material is provided in the valve part of the silicon substrate to apply pretension to the valve part.
JP-A 2001-12356 discloses that a convex part is provided at a central part of a valve part and a ring shaped sealing part is formed at a valve receptor, and when a valve forming member integrally molding the valve part and the valve receiving member formed with the valve receptor are bonded, the convex part of the valve part and the ring shaped sealing part are contacted to each other while being applied with pretension, in order to stabilize the mechanism for preventing back flow in the micropump.
However, in the micropump shown in JP-A 02-308988 in which each members (members constituting the valve part and the pressurized chamber, a valve receiving member bonded with the valve part with pressure, and a vibrating plate vibrated by a piezoelectric element) constituting the micropump are ultrasonically bonded with respect to each other, the bonding precision is low since the base material is only partially dissolved. Further, in the case that each members are adhered using an adhesive, if a component for dissolving the adhesive such as alcohol is contained in a fluid supplied by the micropump, the adhesive is threatened to dissolve into the fluid, thereby changing the properties of the components of the fluid, or stripping off the adhered portions. Further, the adhesive may remain at the interface between the adhered parts during adhesion thus worsening the flow of the fluid. Furthermore, since the adhered region during adherence is unstable, bonding with high accuracy cannot be achieved.
Additionally, in the micropump shown in JP-A 04-63973, when providing the projection of polymeric material at the valve part of the substrate made of silicon, it is required to perform dry etching on the silicon substrate and form the projection by screen printing in an aligned condition with high accuracy, which is troublesome and time consuming because of the complicated steps. Moreover, since the dry etching apparatus is expensive and the silicon material itself is expensive, the manufacturing cost becomes extremely high.
In the micropump shown in JP-A 2001-12356, when manufacturing such micropump, it is impossible to form the convex part or the ring shaped sealing part after bonding the valve forming member and the valve receiving member. Thus, it is required to provide the convex part at the central part of the valve part of the valve forming member in advance, form the ring shaped sealing part at the valve receptor in advance, and thereafter bond the valve forming member and the valve receiving member. As such bonding method, bonding the valve forming material and the valve receiving member under high temperature by a method like diffusion bonding may be conceived, but with such method, a problem arises that tension may be lost in the annealed state. Therefore, in order to prevent the problem, it is required to perform bonding using adhesive under a relatively low temperature or bonding at a limited bonding region excluding the portion provided with pretension, which is, however, followed by another problem that when using the adhesive, the adhesive dissolves into the fluid, the adhered portion may be stripped off, and the flow of the fluid worsens. Further, when bonding is performed for a limited bonding region, the diffusion bonding method cannot be employed, thus necessitating the use of ultrasonic welding or laser welding, which causes a problem to arise that distortion occurs at the border between the bonded portion and the non-bonded region, rendering it impossible to perform bonding with high accuracy.